fix(safe-paths): unlink planted symlinks as the customer, then fail closed

Root rm -f in drop_symlink could be redirected by a parent-directory swap to
delete arbitrary files as root. drop_symlink and the logs/ symlink sweep now
unlink AS THE CUSTOMER (can never delete anything the customer couldn't), and
drop_symlink still refuses to start if the path is a symlink afterwards; the
pre-daemon logs/ gate re-checks and fails closed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/safe-paths.sh

@@ -34,13 +34,14 @@ die() {
   exit 1
 }
 
-# drop_symlink PATH : if PATH is a symlink, unlink it (as root: rm on the final
-# component never touches the link target, and the customer cannot deny it) and
-# log it. Fails closed: if it is still a symlink afterwards, refuse to start.
+# drop_symlink PATH : if PATH is a symlink, unlink it AS THE CUSTOMER (rm on
+# the final component never touches the link target, and if a parent dir is
+# swapped for a symlink mid-way the customer can only delete what they already
+# could) and log it. Fails closed: still a symlink afterwards -> refuse to start.
 drop_symlink() {
   if [ -L "$1" ]; then
     echo "entrypoint: SECURITY: $1 was a symlink to '$(readlink "$1")' - removing" >&2
-    rm -f -- "$1"
+    as_user rm -f -- "$1"
     [ -L "$1" ] && die "could not remove symlink $1"
   fi
   return 0
@@ -59,9 +60,11 @@ secure_home() {
   # public_html may legitimately be a symlink (release-dir deploys); it is left
   # alone and every root-side operation on it runs as the customer instead.
   if [ -d "$h/logs" ]; then
-    # find without -L never follows symlinks; -delete unlinks the link itself.
-    # Errors are not fatal HERE: require_safe_logs re-checks and fails closed.
-    find "$h/logs" -xdev -type l \
+    # As the customer: find without -L never follows symlinks, -delete unlinks
+    # the link itself, and a raced parent swap can only reach what the customer
+    # could already delete. Errors are not fatal HERE: require_safe_logs
+    # re-checks immediately before the daemons start and fails closed.
+    as_user find "$h/logs" -xdev -type l \
       -printf 'entrypoint: SECURITY: %p was a symlink to %l - removed\n' -delete >&2 || true
   fi
 }